The first C-12A models entered service with the U.S. Army in 1974 and was used as a liaison and general personnel transport. The aircraft was essentially an "off-the-shelf" Super King Air 200, powered by the type's standard Pratt & Whitney Canada PT6A-41 engines.[1]

The U.S. Navy followed suit in 1979, ordering a version of the Super King Air A200C (modified with a 52 inch by 52 inch cargo door from the Super King Air 200C), designating it the UC-12B, for logistics support between Naval and Marine Corps air stations, air facilities, and other activities, both in CONUS and overseas. The cabin can readily accommodate cargo, passengers or both. It is also equipped to accept litter patients in medical evacuation missions. Through 1982, the Navy ordered 64 of these aircraft.[1]

A U.S. Air Force variant of the plane for surveillance roles primarily over Afghanistan and Iraq is the MC-12 Liberty. For that variant, Beechcraft builds the basic plane and then sends it to Greenville, Texas where sophisticated Intelligence, Surveillance & Reconnaissance equipment is installed by L-3 Communications Missions Integration.[2] As of 2013 the Liberty program has exceeded 300,000 combat flying hours.[3]

Although the UD- series 1900s were manufactured exclusively for military use, the United States military and other military and government organizations use 1900s from other series such as the UB-series 1900C, and 1900Ds which may be found elsewhere.[7]

U.S. Navy training version developed by conversion of UC-12B airframes.

C-12C

U.S. Army and U.S. Air Force version of the C-12A with upgraded engines. Based on the King Air A200 (serial numbers BC-62 and up).

C-12D

U.S. Army and U.S. Air Force version. Based on the King Air A200CT, changes include larger cargo door, "high-flotation" landing gear (a Beechcraft option for larger main landing gear wheels for use on unimproved runways) (serial numbers BP-1, BP-22, BP-24 through BP-51).

U.S. Navy version based on the King Air B200C (serial number BU-1 and up, BV-1 and up, BW-1 and up). Cockpit upgraded to Proline 21.

RC-12G

U.S. Army version used for real-time tactical intelligence support under the Crazyhorse program.[8] Based on the King Air A200CT (three aircraft, serial numbers FC-1 and up). Previously operated by U.S. Army Reserve aviation units.

RC-12H

Special mission, battlefield SIGINT aircraft for the U.S. Army.

C-12L

Three A200s acquired for use in the Cefly Lancer program as RU-21Js. In 1984 the three aircraft modified with new VIP interiors, and returned to the U.S. Army as C-12Ls.[9]

Note: The U.S. military also operates other King Air versions under other designations, including the C-6 Ute and T-44 series. In addition, there are a number of Beechcraft 1900s operated by the military under civilian registrations, using their civilian model designations.